You seem to be confused about the argument. It's not about what should be, it's about what is.
> So hand-wringing about how people vote in primaries and interact with political parties is silly.
It's not silly, it's an observation about how the game of politics is changing with the change in the scale of our social interactions. It's so much easier to coordinate large groups of people to infiltrate and manipulate intra-party matters than it was a few decades ago.
That's exactly what the OP was advocating: not rational engagement with the members of a party, convincing them to adopt a better view, but pretending to be one of them so as to vote in their primaries, to deny them use of candidates which are most threatening to one's own political goals. It's like a Sybil attack on the political process.
Political parties do not exist in the governing structure of the U.S. As proof, I'll ask you to please go read the Constitution, then come back and point out the parts about political parties. No rush; I'll wait.
Back? Ok, so now hopefully you realize that in the U.S., we elect people, not parties. Partisan primaries, as elections funded by the government, should not even exist at all--they are a corruption of the system.
So hand-wringing about how people vote in primaries and interact with political parties is silly. Political parties can't be corrupted. There is nothing pure to preserve.